Present day safety regulations require industry to periodically test portable lamp holders. The testing is done to verify the wiring polarity and ground continuity in the lamp holders. In some cases there are large numbers of lamp holders which must be tested to satisfy such regulations. Since the sockets of most lamp holders are of the screw type, i.e. the lamp holder accepts a lamp having a screw type base, in the past screw-in adaptors were used to facilitate such testing. Use of screw-in adaptors requires an inordinate amount of time to test lamp holders, especially when a large number of lamp holders must be tested. As a result, the testing of lamp holders is laborious and costly.